化简(1)6xy-10x2-5yx+7x2(2)(3x2-2)-3(4x2-2x-3)+2(2x2-1)(3)先化简,再求值:3x2y-[2x2y-3(2xy-
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化简 (1)6xy-10x2-5yx+7x2 (2)(3x2-2)-3(4x2-2x-3)+2(2x2-1) (3)先化简,再求值:3x2y-[2x2y-3(2xy-x2y)-xy],其中x=-1,y=-2. |
答案
(1)6xy-10x2-5yx+7x2=xy-3x2;
(2)(3x2-2)-3(4x2-2x-3)+2(2x2-1) =3x2-2-12x2+6x+9+4x2-2 =-5x2+6x+5;
(3)3x2y-[2x2y-3(2xy-x2y)-xy]=3x2y-2x2y+6xy-3x2y+xy =-2x2y+7xy, 当x=-1,y=-2时, 原式=-2×(-1)2×(-2)+7×(-1)×(-2)=18. |
举一反三
-a2b-[a2c-(a2c-a2b)-1.5abc]-abc,其中a=-2,b=2,c=3. |
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